Regulators are commonly employed in fluid or gas distribution systems to control the pressure in the system downstream of the regulator. As is known, the pressure at which a typical gas distribution system supplies gas may vary according to the demands placed on the system, the climate, the source of the supply, and/or other factors. However, most end-user facilities equipped with, for example, gas appliances such as furnaces, ovens, etc., require the gas to be delivered in accordance with predetermined pressure parameters. Therefore, such distribution systems use gas regulators to ensure that the delivered gas meets the requirements of the end-user facilities.
Conventional gas regulators generally include a closed-loop control actuator or control assembly for sensing and controlling the pressure of the delivered gas. Many regulators use a pneumatic control assembly having a diaphragm and a sense tube or pitot tube that extends into the outlet side of the regulator. The tube senses, for example, the pressure or other parameters in the downstream or outlet end of the regulator, and communicates that sensed parameter to the control assembly. Based on the sensed parameter, the control assembly makes any needed adjustments to the position of a control element, which then keeps the sensed parameter at a desired value or within an acceptable range.
FIG. 1 depicts an example of a conventional regulator device 10. The regulator device 10 includes a valve body 12 having an inlet 14, an outlet 16, and a valve port 18. A control element 20 is shiftably disposed within the valve body 12, such that the control element 20 can be displaced relative to the valve port 18 in order to control the flow of a fluid between the inlet and the outlet. The regulator device 10 includes a control assembly 22 including a valve actuator 24. The control assembly 22 includes a diaphragm 26, and the control assembly 22 is connected to a valve stem 28 via a suitable linkage assembly 30. The valve stem 28 is connected to the control element 20, such that movement of the valve actuator 24 moves the control element 20 relative to the valve port 18. The control assembly 22 includes a diaphragm chamber 32, which is in flow communication with the outlet 16 via a sense tube 34.
The inlet 14 of the regulator device 10 receives gas from a gas distribution system, for example, and the outlet 16 delivers gas to an end-user facility such as a factory, a restaurant, an apartment building, etc. having one or more appliances. The control assembly 22 and the actuator 24 control the position of the control element 20, and consequently gas flowing through the regulator device 10 flows into the inlet 14, through the valve port 18, and out the outlet 16 to the end-user facility, with the position of the control element 20 thus controlling the flow of gas through the device.
The linkage assembly 30 includes a control arm 36, which in turn is connected to the valve stem 28. The control assembly 22, using the valve actuator 24, regulates the outlet pressure of the regulator device 10 based on the outlet pressure sensed in the outlet 16. Specifically, the control assembly 22 includes a diaphragm support plate 38 coupled to a piston 40, which together move the position of the diaphragm 26, the control arm 36, the valve stem 28, and ultimately the control element 20. The sense tube 34 senses the pressure in the outlet 16. If the sensed pressure is too low, the pressure in the diaphragm chamber 32 drops accordingly by virtue of the flow communication provided by the sense tube 34. Consequently, because the desired control pressure is applied to the piston side of the actuator 24, the pressure differential will cause the diaphragm 26 to move (to the right when viewing FIG. 1), which in turn moves the control element upward when viewing FIG. 1. This opens the valve port more, thus increasing the pressure in the outlet 16. On the other hand, if the sensed pressure is too high, the pressure in the diaphragm chamber is greater than the desired control pressure, and the pressure differential against the diaphragm causes the diaphragm to move to the left when viewing FIG. 1, thus moving the control element closer to the valve seat, which decreases the flow through the valve port. The control assembly 22 further includes a control spring 42 in engagement with a top-side of the control assembly 22 to offset the outlet pressure sensed by the diaphragm 26. Accordingly, the desired outlet pressure, which may also be referred to as the control pressure, is set by the selection of the control spring 42.
Multiple body sizes may be offered for fluid regulator platforms. When the size of the outlet of a regulator device changes, there is a resulting change in how the flow path recovers once gas/fluid has exited the regulator body. Because the outlet of the valve body is where the outlet pressure is sensed, in order to control the regulator it is desirable that the pressure zone remains the same for all body sizes. In real world applications however, it is unreasonable to expect the pressure zone to be stationary in the pipe as the flow path changes. This sensed pressure fluctuation creates areas of increased boost and droop, which may limit overall capacity.
There also exist certain flow conditions caused by the geometry of the flow path that cause the sensed outlet pressure of the regulator to abruptly boost or droop. These pressure spikes may cause the outlet pressure to exceed the required accuracy class. This boost or droop out of the specified accuracy class in turn forces the regulator to be rated at a much lower capacity than if the sensed pressure were to stay constant.